Ok, first of all, it needs to be clarified as to what the "repairman certificate" for an experimental amateur-built aircraft really does. The fact is, it has NOTHING to do with repair, maintenance, or modification of the aircraft. For amateur-built aircraft, the person doing maintenance, repair, or modification does NOT need ANY FAA certificate of any kind. You do not have to be the builder, nor the owner, and you do not have to hold any FAA certificate in order to perform these functions. ANYBODY is authorized. (Ref: 14 CFR 43.1(b))
What the "repairman certificate" actually authorizes the holder to do, and the ONLY thing it authorizes the holder to do, is perform the condition inspection of the aircraft as required by its operating limitations. Right now, for amateur-built aircraft, the only person who is eligible for this "repairman certificate" is the original, primary builder. Again, this person does not need the certificate to repair the aircraft. Only to inspect it in accordance with the operating limitations.
Now, for experimental light-sport aircraft, since these aircraft do not meet the major portion requirements for amateur-built certification, the person applying for the repairman certificate must be the OWNER of the aircraft (and may or may not be the builder). This person must attend and successfully complete a 16 hour course of instruction focused on aircraft INSPECTION. (Like amateur-built aircraft, the person performing maintenance, repair, or modification does not need to hold ANY FAA certificate of any kind.)
What EAA has been working with the FAA on for some time is expanding the regulation to allow subsequent owners of amateur-built aircraft to attend a similar course of instruction as to ELSA owners, so that they too may be eligible for a repairman certificate authorizing them to perform the condition inspections on their aircraft. The course curriculum already exists and is FAA-accepted for ELSA owners. With the proliferation of second owners of amateur-built aircraft, the question has arisen as to why these inspection courses couldn't be expanded to include amateur-built aircraft owners.
So this is a long-winded explanation to illustrate that the course doesn't teach anything about maintenance, repair, or modification. It teaches inspection techniques that can be applied to any airframe or engine. This is well within the scope of authority of the amateur-built aircraft repairman certificate.